A Thermal Expansion Tank is a requirement, by law, when your hot water heater includes a back flow preventer at your water main or a check valve anywhere in your plumbing system. If you have installed a circulation pump anywhere in your house, you have a check valve. Additionally, backflow preventers have become a more prominent addition to codes in various areas. Whenever water is heated, it expands. In the past, excess or expanded water would flow back into the public water system, however backflow preventers stop this from happening, creating a need for a place for that expanded water to go. For example if you have a 40 gallon hot water heater there could be an additional 1/2 gallon of water created even without any demand.
As a homeowner, your hot water heater is not something you look at or check on a regular basis. You install it (or have it installed) and forget about it until one day you have a problem! You may or may not notice a little water coming from your water heater. It could come from the temperature pressure relief valve in the form of just a few drips or a gush of water. The cause for leakage could be linked back to the expansion of the water in the tank and now it has nowhere to go. The purpose of a Thermal Expansion Tank is to act as an overflow for the excess water created by the water heating.
A Thermal Expansion Tank can be added to your hot water tank at any time. It does not need to be done when your are replacing an old tank. But if you are replacing a water heater, you should add a thermal expansion tank!
Typically a Thermal Expansion Tank is a small metal tank - usually either 2.1 gallons or 4.5 gallons. The ZEP1, however, is designed specifically for use with either point of use or tankless water heaters with up to 2 gallons of water volume. The set point for this type of tank is 140°F. It is smaller, about 3" x 4" and constructed of stainless steel. The ZEP1 comes with a factory pre-charge of 50 psi. This may need to be adjusted depending on the water pressure in your home.
Brass plumbing fittings are recommended for installation as they will tend to last longer. The thermal expansion tank is typically installed on the cold water line.